polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are intracellular polyesters produced by many bacteria and some archaea as carbon and energy storage compounds. They accumulate as granules when cells have excess carbon and limited nutrients such as nitrogen or phosphorus. The best known member is polyhydroxybutyrate (PHB); copolymers like PHBV broaden properties.

PHAs consist of hydroxyalkanoate monomers linked by ester bonds. Monomer length ranges from short to medium, yielding different material properties. Biosynthesis begins from acetyl-CoA, involving the enzymes PhaA, PhaB, and PhaC. Genes encoding these enzymes are widespread in PHA producers, including Cupriavidus necator, Bacillus, Pseudomonas, and Halomonas species. Production can use diverse carbon sources, including sugars, lipids, and waste streams.

PHAs are biodegradable and biocompatible. PHB is relatively stiff and brittle, but copolymers such as PHBV and blends can enhance toughness and processability. They are melt-processable with conventional equipment, enabling extrusion and molding for packaging and small devices.

Degradation occurs via microbial depolymerases under aerobic or anaerobic conditions, with rates influenced by composition and environment. Commercial use is challenged by high production costs and competition with cheap plastics. Efforts focus on using inexpensive feedstocks, improving yields, and facilitating recycling.

Applications include packaging, disposable items, and medical devices where biocompatibility matters. PHAs are central to sustainable plastics research and may reduce plastic waste, but widespread adoption awaits further cost reductions and scalable supply chains.